1. Field of the Invention
The present invention relates to a method and a device for automatically turning on and off the headlights of a motor vehicle. The turning on and off of the headlights is carried out taking into consideration the amplitude of the direct-current voltage present between the positive and negative terminals of the electric energy storage battery of the vehicle, which direct-current voltage being applied to the headlights when turned on.
2. Brief Description of the Prior Art
The statistics indicate that the number of major accidents on the roads would be substantially reduced if the motor vehicles would be always drived with their headlights turned on. This would improve the safety on the roads even during sunny days, but especially during nightfall. It would thus be convenient to install on the motor vehicles a system for automatically turning their headlights on and off, whereby such vehicles would be always drived with the headlights on.
A plurality of systems for automatically turning on and off the headlights of a motor vehicle have already been proposed.
As a first example, U.S. Pat. No. 3,262,011 (CONES) issued on July 19, 1966, describes a lighting system comprising a resistor which interconnects the ignition switch of the motor vehicle with the low beam filaments of two headlights. When the manually operated switch normally used to turn the headlights on and off is open, the low beam filaments are supplied through the ignition switch if the latter is closed. The resistor then causes a diminished illumination of the two headlights. Such a system is suitable for both day and night driving.
As a second example, U.S. Pat. No. 3,402,321 (TAGAWA) issued on Sept. 17, 1968, defines a system for switching electric power between the head and parking lights of a motor vehicle. When the vehicle is stationary and the gas pedal released, the parking lights are on while the headlights are off. When the gas pedal is depressed to cause motion of the vehicle, the headlights are turned on and the parking lights turned off through the action of a relay whose coil is energized in response to depression of the gas pedal. A pulse emitter mechanically coupled to the driving shaft of the vehicle delivers a train of pulses having a frequency proportional to the shaft rotational speed. The pulses are supplied to the coil of a relay to keep the headlights on after the gas pedal has been released, and that as long as the driving shaft rotation exceeds a predetermined magnitude.
U.S. Pat. No. 3,702,415 (SCHULTZ) issued on Nov. 7, 1972, proposes a system associated with the light and ignition switches of an automotive vehicle to turn on the vehicle's headlights along with or instead of its parking lights when the manually operated light switch is in its parking light activating position and the vehicle is in an operating condition.
As a fourth example, U.S. Pat. No. 3,706,006 (MILLER, SR) issued on Dec. 12, 1972, discloses a lighting control system for motor vehicles which turns on the lights of the vehicle whenever the vehicle is operated either by day or night for safety purposes. Such a system includes a pressure switch responsive to operation of the vehicle engine to energize through relays the lights of the vehicle regardless of the position of the normal, manually operated lighting switch. The lights are turned off a predetermined time period after the vehicle has been stopped. Switches are also provided to disconnect the lighting control system so that the lights of the vehicle may be turned on and off in a conventional manner.
U.S. Pat. No. 3,774,071 (GOODRICH) issued on Nov. 20, 1973, proposes a conrtrol system for automatically turning on the headlights of a motor vehicle as soon as the engine is turned on, and the oil pressure reaches its normal operating level or the transmission is shifted into a drive position. The headlights are turned off when the ignition is switched off and the engine stops.
U.S. Pat. No. 3,832,597 (MITCHELL) issued on Aug. 27, 1974, describes a light energizing system for compelling all the running lights of a motor vehicle to be energized, with the definite exception of the high beam headlights, whenever, day or night, the ignition switch is placed in running position and the transmission is set for forward drive.
As a last example, U.S. Pat. No. 4,337,400 (HAHN) issued on June 29, 1982, discloses an automatic headlight control system for a motor vehicle. When the vehicle ignition is on, turning the windshield wiper switch on causes energization of a switching relay to turn the headlights on, while turning the windshield wiper switch off causes the switching relay to be de-energized to turn the headlights off. Turning the ignition switch off causes both turning off of the headlights and windshield wipers.
As can be seen, none of the above-discussed prior art systems for automatically turning on and off the headlights of a motor vehicle takes into consideration the amplitude of the direct-current voltage present between the positive and negative terminals of the electric energy storage battery of the vehicle.
The amplitude of the direct-current voltage present between the positive and negative terminals of the electric energy storage battery of a motor vehicle (which direct-current voltage being applied to the vehicle's headlights when turned on) may be reduced due, for example, to starting of the engine of the vehicle, to the use of booster cables to supply electric energy from the battery to another vehicle for the purpose of starting the engine of the latter, and to very low temperatures. On the other hand, the amplitude of the direct-current voltage may be increased, for example, during charging of the battery by the alternator of the vehicle after a long engine starting operation, during power boosting of the battery by the electric energy storage battery of another motor vehicle, and during malfunctioning or testing of the alternator.
As the amplitude of the direct-current voltage appearing between the positive and negative terminals of the electric energy storage battery of a motor vehicle may vary as discussed hereinabove, a system for automatically turning on and off the headlights of a vehicle may be advantageously designed to turn the headlights on only when the amplitude of the direct-current voltage is located within a predetermined range of voltage amplitudes, i.e. when the direct-current voltage is higher than a first predetermined voltage amplitude in order to protect the battery, and when the battery direct-current voltage is lower than a second predetermined voltage amplitude higher than the first one to protect the headlights. Under these conditions, the headlights are not supplied with electric power when the direct-current voltage is too low (in order to protect the battery), and the headlights cannot be subjected to a too high direct-current voltage, so as to protect the same.